Our objective is a generalized understanding of the mechanisms by which oxygen supports life, in terms of the structures of oxidases, oxygenases, and mixed function oxidases, of oxygen and substrates, and of the mechanisms of oxygen activating enzymic reactions. We propose to investigate selected dioxygenases, mixed function oxidases and electron transfer oxidases, primarily those with copper, iron, (non-heme) or heme as prosthetic groups. We propose to continue our biochemical and biophysical studies by (1) investigating the structures of active sites and related protein structures of copper and heme oxidases; (2) characterizing the reactions which take place at the active sites of these oxidases with oxygen and substrates, and reducing cofactors if any; (3) attempting to observe the metastable and reactive forms of oxygenated enzyme complexes by seeking new techniques for forming, detecting, and characterizing functional enzyme complexes with oxygen, substrates, and cofactors, particularly in the direction of cryoenzymological methods; (4) formalizing our generalized understanding of oxidase structures and mechanisms.